It is not permissible to buy a product then sell it when it is still in the warehouse of the first vendor, before it has been moved
It is not permissible for the purchaser of this product to sell it so long as it is still in the possession of the seller, until the purchaser has taken possession of it and moved it to his house or the marketplace, because of the saheeh ahaadeeth that have been narrated from the Prophet (peace and blessings of Allaah be upon him) concerning that. For example, he (peace and blessings of Allaah be upon him) said: “It is not permissible to sell something on condition that the purchaser lend you something, and it is not permissible to have two conditions in one transaction, and no profit is permissible unless possession has been taken of the goods, and you cannot sell what is not in your possession.” Narrated by Ahmad and the authors of al-Sunan with a saheeh isnaad.
And he (peace and blessings of Allaah be upon him) said to al-Hakeem ibn Hizaam: “Do not sell that which you do not have.” Narrated by the five except Abu Dawood, with a jayyid isnaad.
And it was narrated from Zayd ibn Thaabit (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) forbade selling a product in the place where it was bought until the merchants have taken possession of it and moved it to their own property. Narrated by Ahmad and Abu Dawood; classed as saheeh by Ibn Hibbaan and al-Haakim.
Similarly, if a person buys from the purchaser, it is not permissible for him to sell it until he transfers it to his house or to another place in the marketplace, because of the ahaadeeth quoted and other ahaadeeth which convey the same meaning. And Allaah is the Source of strength.